The overall objective of this research proposal is to more fully understand the mechanisms regulating the control of cell division, and thus the molecular processes affected during malignant cell growth. IN S. cerevisiae, nine cyclically produced proteins, the cyclins, control the activity/specificity of the cell cycle regulator Cdc28. During the G1 phase of the cell cycle, the first of four waves of cyclin gene expression occur and are controlled by ECB's. ECB's are bound by the transcription factor Mcm1, however, we believe there are other proteins in addition to Mcm1 that regulate ECB activation and mediate the expression of cyclin genes specifically during G1. To identify new Mcm1 interacting protein (s) associated with G1 progression, we will mutagenize MCM1 by PCR mutagenesis then identify mutants that are specifically defective in ECB transcription. These will be further characterized and used to help identify other proteins involved in ECB regulation. In addition, since ECB regulated genes play a key role in size control and initiation of DNA synthesis, we will attempt to identify mutants that affect both size control and chromosome transmission fidelity. Thus we propose to screen for mutants that affect both processes as a means of identifying novel regulators of this pathway.